The “cath lab” in a hospital is where a patient is injected with a radiocontrast media, imaged, diagnosed, and often operated on. Typically, a cardiologist refers the patient to the cath lab and the patient is instructed not to eat or drink the night before. In the case of a patient suffering a heart attack, the patient may be transferred directly to the cath lab.
Often, the patient is dehydrated when the patient arrives at the cath lab. The patient is prepped and the radiocontrast media injected. If, after diagnostic imaging, a possible problem is detected, intervention occurs in the form of angioplasty or the placement of a stent. During these procedures, additional radiocontrast media may be injected into the patient and the patient imaged so the interventional cardiologist or radiologist can view the progress of the operation.
Unfortunately, the radiocontrast media can be toxic to the patient especially a patient who is dehydrated at the time the radiocontrast media is injected. A patient who already suffers from various medical problems such as diabetes or kidney problems is even more prone to medical problems due to the injection of the radiocontrast media.
It has been observed that dehydration increases the risk of contrast induced nephropathy (CIN) when radiocontrast agents are injected into a patient during coronary and peripheral vascular catheterization procedures. CIN is the third most common cause of hospital-acquired renal failure. It occurs in over 5% of patients with any baseline renal insufficiency and can occur in 50% of patients with preexisting chronic renal insufficiency and diabetes. Radiocontrast media has a variety of physiologic effects believed to contribute to the development of CIN. One of the main contributors is renal medullary ischemia, which results from a severe, radiocontrast-induced reduction in renal/intrarenal blood flow and oxygen delivery. The medullary ischemia induces ischemia and/or death of the metabolically active areas of the medulla responsible for urine formation, called the renal tubules. Medullary ischemia is attributed to the increase of oxygen demand by the kidney struggling to remove the radiocontrast media from blood plasma and excrete it from the body at the same time as the normal process of controlling the concentration of urine. Oxygen consumption in the medulla of the kidney is directly related to the work of concentrating urine. Since the presence of radiocontrast media in the urine makes it much more difficult for the kidney to concentrate urine, the work of the medulla outstrips the available oxygen supply and leads to medullary ischemia.
Although the exact mechanisms of CIN remain unknown, it has been consistently observed that patients with high urine output are less vulnerable to contrast injury. It is also clear that dehydration increases the risk of CIN, likely because urine (and contrast media inside the kidney) is excessively concentrated. As a result, patients predisposed to CIN are hydrated via intravenous infusion of normal saline before, during and after the angiographic procedure. Hydration is commonly performed at a conservative rate, especially in patients with existing heart and kidney dysfunction, since over-hydration can result in pulmonary edema (fluid in the lungs), shortness of breath, the need for intubation, and even death. Thus, the patients at highest risk for CIN are those least likely to receive the only proven therapy for preventing CIN (I.V. hydration) due to the unpredictability of side effects from I.V. hydration.
A major limitation to the more widespread use of the already known therapeutic, or optimal, levels of I.V. hydration is the current inability to balance the amount of fluid going into the patient to the amount of fluid being removed or excreted from the patient. It is possible to have a nurse measure a patient's urine output frequently but this method is impractical as nurses are often responsible for the care of many patients. In addition, the only accurate method of measuring urine output is to place a catheter into the patient's urinary bladder. Without a catheter, the patient must excrete the urine that may have been stored in the bladder for several hours. During this time, the amount of I.V. hydration can be significantly less than the amount of urine produced by the kidneys and stored in the bladder, leading to dehydration. Since many patients do not normally have such a catheter during procedures using radiocontrast media, a valid measurement of urine output is not possible.
There seems to be indisputable scientific evidence that CIN in patients with even mild baseline renal insufficiency can lead to long term complications and even increased risk of mortality. This scientific knowledge has not yet been extended to daily clinical practice as routine monitoring of renal function post-catheterization is not usually performed and limits the identification of the known short-term clinical complications.
At the same time, there is a great deal of awareness in clinical practice that patients with serious renal insufficiency (serum creatinine (Cr)≧2.0) often suffer serious and immediate damage from contrast. Many cardiologists go considerable length to protect these patients including slow, overnight hydration (an extra admission day), administration of marginally effective drugs, staging the procedure, or not performing procedures at all.
There are approximately 1 million inpatient and 2 million outpatient angiography and angioplasty procedures performed in the U.S. per year (based on 2001 data). Based on the largest and most representative published studies of CIN available to us (such as Mayo Clinic PCI registry of 7,586 patients) we believe that 4% of patients have serious renal insufficiency (Cr≧2.0). This results in the initial market potential of 40 to 120 thousand cases per year from interventional cardiology alone. There is also a significant potential contribution from peripheral vascular procedures, CT scans and biventricular pacemaker leads placement. As the awareness of the CIN increases, the market can be expected to increase to 15% or more of all cases involving contrast.
According to the prior art, hydration therapy is given intravenously (I.V.) when someone is losing necessary fluids at a rate faster than they are retaining fluids. By giving the hydration therapy with an I.V., the patient receives the necessary fluids much faster than by drinking them. Also, dehydration can be heightened by hyperemesis (vomiting), therefore the I.V. method eliminates the need to take fluids orally. An anesthetized or sedated patient may not be able to drink. Hydration is used in clinical environments such as surgery, ICU, cathlab, oncology center and many others. At this time, hydration therapy is performed using inflatable pressure bags and/or I.V. pumps. A number of I.V. pumps on the market are designed for rapid infusion of fluids (as opposed to slow I.V. drug delivery) for perioperative hydration during surgery, ICU use and even emergency use for fluid resuscitation.
An infusion pump is a device used in a health care facility to pump fluids into a patient in a controlled manner. The device may use a piston pump, a roller pump, or a peristaltic pump and may be powered electrically or mechanically. The device may also operate using a constant force to propel the fluid through a narrow tube, which determines the flow rate. The device may include means to detect a fault condition, such as air in, or blockage of, the infusion line and to activate an alarm.
An example of a device for rapid infusion of fluids is the Infusion Dynamics (Plymouth Meeting, Pa.) Power Infuser. The Power Infuser uses two alternating syringes as a pumping engine. Since it is only intended to deliver fluids (not medication), the Power Infuser has accuracy of 15%. It provides a convenient way to deliver colloid as well as crystalloid for hydration during the perioperative period among other possible clinical settings. The Power Infuser provides anesthesiologists with the ability to infuse at rates similar to that seen with pressure bags, but with more exact volume control. The maximum infusion rate is 6 L/hr. It has the flexibility of infusing fluid at 0.2, 1, 2, 4 and 6 L/hr. A bolus setting of 250 mL will deliver that volume in 2.5 min. In a large blood loss surgical case, the use of Power Infuser enables large volumes of colloid to be delivered to restore hemodynamics.
It is also known in the art that loop diuretics such as Lasix (furosemide) reduce sodium reabsorption and consequentially reduce oxygen consumption of the kidney. They also reduce concentration of contrast agents in the urine-collecting cavities of the kidney. They induce diuresis (e.g., patient produces large quantities of very dilute urine) and help remove contrast out of the kidney faster. Theoretically, they should be the first line of defense against CIN. In fact, they were used to prevent CIN based on this assumption until clinical evidence suggested that they were actually deleterious. More recently, doubts have been raised regarding the validity of those negative clinical studies.
In two clinical studies by Solomon R., Werner C, Mann D. et al. “Effects of saline, mannitol, and furosemide to prevent acute decreases in renal function induced by radiocontrast agents”, N Engl J Med, 1994; 331:1416-1420 and by Weinstein J. M., Heyman S., Brezis M. “Potential deleterious effect of furosemide in radiocontrast nephropathy”, Nephron 1992; 62:413-415, as compared with hydration protocol, hydration supplemented with furosemide adversely affected kidney function in high-risk patients given contrast. Weinstein et al. found that furosemide-treated subjects lost 0.7 kg on average, whereas a 1.3-kg weight gain was noted in patients randomized to hydration alone, suggesting that in furosemide-treated subjects the hydration protocol has been insufficient and patients were dehydrated by excessive diuresis.
The clinical problem is simple to understand: diuresis is widely variable and unpredictable but the fluid replacement (hydration) at a constant infusion rate is prescribed in advance. To avoid the risk of pulmonary edema, fluid is typically given conservatively at 1 ml/hr per kg of body weight. The actual effect of diuretic is typically not known for 4 hours (until the sufficient amount of urine is collected and measured) and it is too late and too difficult to correct any imbalance. Meanwhile, patients could be losing fluid at 500 ml/hour while receiving the replacement at only 70 ml/hour. The effects of forced diuresis without balancing are illustrated in the research paper by Wakelkamp et. al. “The Influence of Drug input rate on the development of tolerance to flrosemide” Br J Clin. Pharmacol. 1998; 46: 479-487. In that study, diuresis and natriuresis curves were generated by infusing 10 mg of I.V. furosemide over 10 min to human volunteers. From that paper it can be seen that a patient can lose 1,300 ml of urine within 8 hours following the administration of this potent diuretic. Standard unbalanced I.V. hydration at 75 ml/h will only replace 600 ml in 8 hours. As a result the patient can lose “net” 700 ml of body fluid and become dehydrated. If such patient is vulnerable to renal insult, they can suffer kidney damage.
To illustrate the concept further, the effects of diuretic therapy on CIN were recently again investigated in the PRINCE study by Stevens et al. in “A Prospective Randomized Trial of Prevention Measures in Patients at High Risk for Contrast Nephropathy, Results of the PRINCE. Study” JACC Vol. 33, No. 2, 1999 February 1999:403-11. This study demonstrated that the induction of a forced diuresis while attempting to hold the intravascular volume in a constant state with replacement of urinary losses provided a modest protective benefit against contrast-induced renal injury, and importantly, independent of baseline renal function. This is particularly true if mean urine flow rates were above 150 ml/h. Forced diuresis was induced with intravenous crystalloid, furosemide, and mannitol beginning at the start of angiography.
The PRINCE study showed that, in contrast to the Weinstein study, forced diuresis could be beneficial to CIN patients if the intravascular volume was held in a constant state (no dehydration). Unfortunately, there are currently no practical ways of achieving this in a clinical setting since in response to the diuretic infusion the patient's urine output changes rapidly and unpredictably. In the absence of special equipment, it requires a nurse to calculate urine output every 15-30 minutes and re-adjust the I.V. infusion rate accordingly. While this can be achieved in experimental setting, this method is not possible in current clinical practice where nursing time is very limited and one nurse is often responsible for monitoring the care of up to ten patients. In addition, frequent adjustments and measurements of this kind often result in a human error.
Forced hydration and forced diuresis are known art that has been practiced for a long time using a variety of drugs and equipment. There is a clear clinical need for new methods and devices that will make this therapy accurate, simple to use and safe.
In addition, patients involved with a variety of medical procedures such as cardiac surgery often retain water. Some patients, such as heart failure patients, may be overloaded with fluid. Often, a diuretic such as Lasix is administered and a nurse is directed to check when the patient has expelled a certain amount of urine. Often, the patient is weighed to determine the amount of fluid loss.
Nurses, however, are often very busy and it is possible that a patient, once given a diuretic, could expel urine to the point the patient becomes dehydrated. Also, to prevent dehydration, the nurse may administer a hydration fluid such as saline. There is no known prior art system which achieves automatic balanced hydration in a patient. The applicant's co-pending applications directed to a balanced hydration system are incorporated herein by this reference. They are U.S. patent application Ser. No. 10/936,945 filed Sep. 9, 2004 entitled “Patient Hydration System and Method”; U.S. patent application Ser. No. 11/408,851 filed Apr. 21, 2006 entitled “Patient Hydration System With a Redundant Monitoring of Hydration Fluid Infusion”; U.S. patent application Ser. No. 11/408,391 filed Apr. 21, 2006 entitled “Patient Hydration System With Abnormal Condition Sensing”; U.S. patent application Ser. No. 11/409,171 filed Apr. 21, 2006 entitled “Patient Hydration System With Hydration State Detection”; and U.S. patent application Ser. No. 11/580,354 filed Oct. 13, 2006 entitled “Patient Connection System For a Balance Hydration Unit”.
One of the purposes of balanced hydration therapy in accordance with these co-pending patent applications is to achieve and maintain a high urine flow. Continuing to induce fluid to balance the patient's urine output causes the patient to continue to urinate at a high rate. Sometimes, there may be a delay between the infusion of saline and urine production. Therefore, if fluid infusion is stopped abruptly, such as at the end of therapy, the patient's urine output rate can continue to be high for some time. This risks dehydrating the patient as the high urine flow can continue with no infusion to balance it. This high urine rate can also be uncomfortable for a patient if he is discharged immediately following therapy.
A similar clinical situation exists in the case of a patient having a physiologic high urine flow that needs to be balanced with replacement fluid. In such situations, reducing urine flow without causing dehydration is often desired. Again, when balancing is stopped abruptly, the result can be dehydration or patient discomfort.
Additionally, a clinical situation exist where a net fluid removal from the patient may be desired. Fluid overload can be caused by a number of factors, among them congestive heart failure, and significant fluid infusion during surgery. The fluid often needs to be removed as quickly and as safely as possible without causing electrolyte imbalance or dehydration.